Field of the Invention
The aspect of the embodiments relates to a position detection device, a position detection method, and a storage medium that are particularly suitable to be used for acquiring a three-dimensional position of an object with a plurality of cameras.
Description of the Related Art
One method is conventionally known where a plurality of cameras is arranged in a monitoring area in a monitoring camera system and simultaneously captures the same object, so that a three-dimensional (hereinafter, referred to as 3D) position of the object can be estimated. For example, Japanese Patent Application Laid-Open No. 2011-511427 and Japanese Patent Application Laid-Open No. 2008-228582 each discuss a method of utilizing stereoscopy to estimate the 3D position of an object based on positions and orientations of cameras and a position of the object on a camera image. Japanese Patent Application Laid-Open No. 2014-238674 discusses a method of estimating a standing position of a person by using an average height of persons determined in advance and a camera parameter obtained by performing camera calibration.
As described above, in the method in each of PCT International Publication No. WO/126071 and Japanese Patent Application Laid-Open No. 2010-63001, stereoscopy is utilized to estimate the 3D position of the object with the plurality of cameras. In a situation where an object is monitored with a single camera alone, the stereoscopy is difficult to utilize, and thus accuracy in the estimation of the position of the object is low.
For example, the situation where the object is monitored with a single camera alone arises when a small number of cameras is arranged in a monitoring area. In such a case, the monitoring area is likely to include portions where fields of view of a plurality of cameras do not overlap. The situation where the object is monitored with a single camera alone might arise even when the fields of view of the plurality of cameras overlap, due to object detection failure or because an object is hidden by another object. Thus, a large number of cameras is to be arranged in the monitoring area to prevent the situation where the object is monitored with a single camera alone from arising.
In the method discussed in Japanese Patent Application Laid-Open No. 2014-238674, the standing position is estimated by using the average height of persons determined in advance. Thus, the accuracy in the estimation of the object position is largely degraded when a person with a body frame significantly different from the average or a child is monitored. Furthermore, the position estimation error increases as a straight line, connecting between the camera and the head of a person, becomes closer to being horizontal, even when the person has an average height.